Transmissive data storage media and an optical head using holographic or acousto-optical deflection

ABSTRACT

An optical data storage system includes an optical data storage system for use with a data storage medium. The system includes a stationary optical head for steering an incident laser beam holographically and/or by means of an acousto-optical method across the data storage medium. The incident laser beam is selectively reflected by the data storage medium to indicate the type of data bits recorded on the storage medium. In a preferred embodiment the optical head includes a laser source for irradiating a collimated laser beam, a beam steering element for steering the laser beam; a beam splitter for deflecting the reflected laser beam; and a photo-detector for detecting the relative intensity of the deflected laser beam for determining the type of recorded data bits. The data storage system may be optically transmissive or partly transmissive.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation-in-part of thefollowing patent applications by the same applicant herein, assigned tothe same assignee, all of which are incorporated herein by reference:

Ser. No. 08/779,461, filed on Jan. 7, 1997, titled "Optical andMagneto-Optical Data Storage Systems Using Transmissive Media";

Ser. No. 08/779,462, filed on Jan. 7, 1997, now abandonded, titled"Stationary Optical Head Using Holographic or Acousto-OpticalDeflection";

Ser. No. 08/779,463, filed on Jan. 7, 1997, now U.S. Pat. No. 5,740,148,titled "Stationary Optical Data Storage System Using Holographic orAcousto-Optical Deflection"; and

Ser. No. 08/779,394, filed on Jan. 7, 1997, now U.S. Pat. No. 5,742,581,titled "Transmissive Optical and Magneto-optical Data Storage Media".

FIELD OF THE INVENTION

This invention relates generally to optical and magneto-optical datastorage systems, and in particular to a transmissive optical andmagneto-optical data storage medium and an optical head usingholographic and/or acousto-optical deflection.

DESCRIPTION OF RELATED ART

Optical and magneto-optic data storage systems store great quantities ofdata on a disk. The data is accessed by focusing a laser beam onto thedisk and detecting the reflected light beam. Three kinds of systems arewell known. The first kind is a ROM (Read Only Memory) system in whichdata is permanently embedded as marks in the disk. The data is detectedas a change in reflectivity as the laser beam impinges on the datamarks.

The second kind is a WORM (Write-Once-Read-Many) system that allows theuser to write data by making marks, such as pits, on a blank opticaldisk surface. Once the data is recorded onto the disk it cannot beerased. The data in a WORM system is also detected as a change inreflectivity.

The third kind is a WREM (Write-Read-Erase-Many) system in which a laserbeam is used to heat a magneto-optic data layer to a criticaltemperature, generally just below the Curie temperature, in order towrite and erase the data. As the critical temperature is reached, themagnetic domain field strength is reduced to close to zero. An externalmagnetic field, using an electromagnet or a permanent magnet, is thenused to reverse the domain to record a one or a zero. In general data isrecorded by orienting the magnetic domain of a spot in either an up or adown position. The WREM system reads the recorded data by directing alow power (reading) laser beam to the data layer. The difference inmagnetic domain directions causes the plane of polarization of the lightbeam to be rotated one way or the other, clockwise or counterclockwise.This change in orientation of polarization is then detected andrecognized as either a digit "1" or "0".

U.S. Pat. No. 5,255,262 to Best et al., titled "Multiple Data SurfaceOptical Data Storage System With Transmissive Data Surfaces", issued onOct. 19, 1993, which is incorporated herein by reference, describes anoptical data storage system that includes a multiple data surface mediumand an optical head. The medium includes several substrates that areseparated by a light transmissive medium. With the exception of the lastdata layer, data surfaces are substantially light transmissive and arelocated on the substrate surfaces which lie adjacent to a lighttransmissive medium. The optical head includes an aberration compensatorto allow the head to focus onto the different data surfaces, and afilter to screen out unwanted reflected light.

This patented system is relatively complicated and its manufacture islabor intensive. Also, the system uses a focusing mechanism, which addscomplexity and cost, and reduces the system signal to noise ratio.

Therefore, there is still a greatly unsatisfied need for an optical anda magneto-optical data storage systems that reduce the number ofcomponents, thus simplifying the overall structure, reducing its cost,and improving its performance.

SUMMARY OF THE INVENTION

In a preferred embodiment of the present invention, an optical datastorage medium transmissive to a laser beam is formed of a lighttransmissive substrate that provides mechanical support, and a lighttransmissive data substrate formed on the substrate. The data substrateis patterned to form block regions that block the laser beam frompassing through, and pass regions that allow the laser beam to passthrough, such that the blockage or passage of light through the opticalstorage medium reflects the type of data bits to be stored on theoptical medium.

In another embodiment a magneto-optical data storage medium which isalso transmissive to a laser beam includes a data magneto-optical datasubstrate formed on a substrate. The data substrate is recordable bypatterning a magnetic domain with magnetic fields of different (i.e.,opposite) directions, such that each magnetic direction reflects thetype of data bits to be stored on the optical medium. In yet anotherembodiment the data substrate includes a combination of block and passregions as well as one or more writeable and/or recordable films.

In an embodiment of the present invention the optical data storagesystem includes an optical data storage system for use with a datastorage medium. The system includes a stationary optical head forsteering an incident laser beam holographically and/or by means of anacousto-optical method across the data storage medium. The incidentlaser beam is selectively reflected by the data storage medium toindicate the type of data bits recorded on the storage medium. In apreferred embodiment the optical head includes a laser source forirradiating a collimated laser beam, a beam steering element forsteering the laser beam; a beam splitter for deflecting the reflectedlaser beam; and a photo-detector for detecting the relative intensity ofthe deflected laser beam for determining the type of recorded data bits.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention and the manner of attaining them,will become apparent, and the invention itself will be understood byreference to the following description and the accompanying drawings,wherein:

FIG. 1 is a schematic diagram of an optical system according to thepresent invention;

FIG. 2 is a partial cross-sectional view of an optical data storagemedium according to the present invention, for use with the opticalsystem of FIG. 1;

FIG. 3 represents a data pattern corresponding to block and pass regionsforming part of the optical medium of FIG. 2;

FIG. 4 is a partial cross-sectional view of another optical data storagemedium according to the present invention, for use with the opticalsystem of FIG. 1;

FIG. 5 is a partial cross-sectional view of yet another optical datastorage medium according to the present invention, for use with theoptical system of FIG. 1;

FIG. 6 is a schematic diagram of a magneto-optic system according to thepresent invention;

FIG. 7 is a partial cross-sectional view of a magneto-optic data storagemedium according to the present invention, for use with themagneto-optic system of FIG. 6;

FIG. 8 is a partial cross-sectional view of a combination optical andmagneto-optic data storage medium according to the present invention,for use with the optical system of FIG. 1 and the magneto-optic systemof FIG. 6;

FIG. 9 is a schematic view of an optical data storage system accordingto the present invention;

FIG. 10A is an enlarged view of part of the optical data storage systemof FIG. 1 showing an exaggerated, detailed, cross-sectional view alongline 2--2 of a data storage medium used in the optical data storage ofFIG. 1;

FIG. 10BB is an enlarged view of part of the optical data storage systemof FIG. 1 showing an exaggerated, detailed, cross-sectional view alongline 2--2 of another data storage medium used in the optical datastorage of FIG. 1;

FIG. 11 is a schematic view of an optical data storage system accordingto the present invention;

FIG. 12 is an enlarged view of part of the optical data storage systemof FIG. 11 showing an exaggerated, detailed, cross-sectional view of adata storage medium used in the optical data storage of FIG. 11 alongline 2--2;

FIG. 13 is an enlarged perspective view of an acousto-optical crystal orphoto-refractive crystal forming part of a beam steering element of theoptical storage system of FIGS. 11 and 12, for controlling an opticalbeam deflection in the X direction;

FIG. 14 is a front plan view of the acousto-optical crystal orphoto-refractive crystal of FIG. 13;

FIG. 15 is an enlarged perspective view of the acousto-optical crystalor photo-refractive crystal of FIG. 13, for controlling an optical beamdeflection in the Y direction;

FIG. 16 is a top view of the acousto-optical crystal or photo-refractivecrystal of FIG. 15;

FIG. 17 is a schematic view of an alternative beam steering element ofthe optical storage system of FIGS. 11 and 12, for controlling theoptical beam deflection in the X and Y directions; and

FIG. 18 is a schematic view of the optical data storage systemillustrating additional structural details.

Similar numerals refer to similar elements in the drawings. It should beunderstood that the sizes of the different components in the figures maynot be in exact proportion, and are shown for visual clarity and for thepurpose of explanation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an optical data storage system 10according to the present invention. The system 10 includes an opticaldata storage medium such as a CD ROM, a WORM, or a WREM disk 12. Animportant characteristic of the disk 12 is that it is partly orcompletely optically transmissive for allowing a laser or light beam topass through. The disk 12 is removably mounted on a spindle 14. Thespindle 14 is rotatably secured to a motor 16 which, in turn, is securedto a chassis 18. The motor 16 rotates the spindle 14 as well as the disk12 around an axis in the direction of the arrow A.

The system 10 further includes an optical head 20 composed of twooptical arms 22, 24 secured to a platform 26 which is movably mounted onthe chassis 18. The first optical arm 22 is positioned below the disk12, and the second optical arm 24 is positioned above the disk 12, inregistration with the first optical arm 22. It should be understood thatin another embodiment the positions of the optical arms 22, 24 relativeto the disk 12 may be reversed.

The first optical arm 22 is formed of a light source 31 such as a lasersource, which is distally connected to a first reflective mirror M1 viaa link 32. The second optical arm 24 is formed of a second reflectivemirror M2 which is distally connected to a photo-detector 33 via a link35. The mirrors M1 and M2 are capable of traveling between an innermosttrack referred to as the inner diameter (ID) track, and an outermosttrack referred to as the outer diameter (OD) track.

In operation, the optical head 20 moves radially, i.e., linearactuation, relative to the disk 12, in the direction of the arrow B. Itshould be clear to a person skilled in the art that the optical head 20may alternatively be moved pivotally, i.e., rotary actuation. The lasersource 31 generates a light or laser beam 37 substantially parallel tothe surface of the disk 12. The laser beam 37 impinges upon the firstmirror M1 and is reflected thereby toward the disk 12.

As further illustrated in FIG. 2 the laser beam 37 either passes throughthe transmissive disk 12, where it impinges on a transparent region ofthe disk 12, for indicating a digit "1". The laser beam 37 is diffracted(or reflected) by the disk 12 where it impinges on a diffractive (orreflective) layer or region, for indicating a digit "0". When the laserbeam 37 passes through the disk 12 it is captured by the second mirrorM2 and reflected thereby to the photo-detector 33 for processing.

The optical system 10 offers several advantages over existing systems.For instance, the optical system 10 eliminates the requirement for afocusing mechanism, thus reducing the number of components, simplifyingthe system manufacture and operation and improving its performance, andreducing its overall cost. In addition, the optical medium or disk 12 issimpler and less expensive to produce.

FIG. 2 is a cross-sectional view of the optical data storage medium ordisk 12 according to the present invention. The disk 12 includes asubstrate 40 which is transmissive either fully or partly to the laserbeam 37 (FIG. 1). The substrate 40 provides mechanical support to thedisk 12, and is generally deposited where the laser beam 37 enters thedisk 12. The substrate 40 may be made of glass, polycarbonate or anothersuitable polymer material. In one embodiment the thickness of thesubstrate 40 ranges between 1 mm and 2 mm.

A data substrate 42 is then formed, deposited on, or bonded to thesubstrate 40. The data substrate 42 is preferably fully transmissive tothe laser beam 37, but may also be partially transmissive. The datasubstrate 42 may be of the same material as the substrate 40. In oneembodiment the substrate 40 and the data substrate 42 form a singleintegral layer. The partial transmissiveness of the data substrate 42may be preferred for cost reason.

The data substrate 42 is patterned to form block regions, e.g., 43, 44,45,46 and pass regions, e.g., 50, 51, 52, 53, 54. The block regions donot allow the light beam to pass through. For instance block region 44is shown as blocking light beam 37 from passing through the datasubstrate 42 by reflecting it. The pass regions on the other handprovide an optical path for the light beam 37 through the data substrate42.

The blockage, or the passage of the light beam 37 through the disk 12,indicate the type of binary digit "1" or "0" recorded or stored on thedisk 12. For instance, in one embodiment the block region indicates thatthe digit "0" has been recorded, while the pass region indicates thatthe digit "1" has been recorded. In another embodiment the block regionindicates that the digit "1" has been recorded, while the pass regionindicates that the digit "0" has been recorded.

FIG. 3 represents a data pattern corresponding to the block and passregions of FIG. 2. Starting at block regions 43, 44, the data patternindicates that two consecutive "0" digits are recorded on the disk 12.Pass region 51 shows a "1"; block region 45 reflects a "0"; the twoconsecutive pass regions 52, 53 indicate two consecutive digits "1";block region 46 indicates a "0"; and pass region 54 indicates a "1". Thelength of a region block and that of a pass region are substantiallysimilar, and are generally representative of a single bit of data.

In a preferred embodiment after the data substrate 42 is deposited on,and bonded to the substrate 40 the block regions are formed by etchingaway part of the substrate 42 to form corresponding wells. The wells maybe hollow or filled with an appropriate material, and may be formed bymeans of well known techniques such as photo-etching, or techniques tobe developed in the future. While FIG. 2 shows that the block regionsare etched throughout the entire depth of the data substrate 42, itshould be understood that the block regions may be etched to apredetermined depth that is less than the entire depth of the datasubstrate 42. In addition, while FIG. 2 shows that all the wells of theblock regions have a similar depth, it should be clear that in adifferent embodiment the wells of the block regions may have varyingdepths across the surface of the disk 12.

After the wells are formed, their bottom surfaces are coated withreflective coatings, e.g., 60, 61, 62. These reflective coatings 60, 61,62 may be made of any suitable reflective material such as aluminummetal with a thickness of approximately 50 nm. In the embodiment of FIG.2 the upper surface 65 of the data substrate is not protected by aprotective layer. In an alternative embodiment a protective layer (notshown) may be formed over the upper surface 65. The reflective coatingsmay be smooth to reflect the laser beam 37, or they may have roughenedincident surfaces in order to diffract the laser beam 37.

FIG. 4 is a cross-sectional view of an alternative embodiment for anoptical data storage medium or disk 70 according to the presentinvention, for use with the optical system 10 of FIG. 1. The disk 70 issimilar to the disk 12 and includes a substrate 40 on which a datasubstrate 71 with a plurality of pass regions 50-54 are formed. The datasubstrate 71 may be made from the same material as the substrate 40. Thedata substrate 71 further includes a plurality of block regions, e.g.,72, 73, 74, 75, that are patterned to reflect or diffract the storeddata.

In this disk 70 the depth of some or all the block regions do not extendall the way through the data substrate 71. In a preferred embodimenteach block region, for instance block region 74, is formed by depositinga reflective layer 80 at the bottom of the well, in proximity to thegeometric center plane of the data substrate 71. It should however beunderstood that in other embodiments the reflective layer 80 may beformed at any depth of the data substrate 71. As illustrated in FIG. 5,the reflective layers 72-75 may be formed in proximity to the uppersurface 83 of the disk 70. A combined design of the various depthpositioning of the reflective layers 72-75 is also possible.

An optional but desirable protective layer 85 is deposited on top of theupper surface 83. This will enable the data stored on the disk 70 to beread from either side of the disk 70. The solid lines indicative of thelaser beam 37 illustrate that the laser beam 37 can be incident fromabove the disk 70 to read the data. The dashed lines indicative of thelaser beam 37A illustrate that the laser beam 37A can alternatively beincident from underneath the disk 70.

In a preferred embodiment the optical disk 12 is between 1 mm to 1.2 mmthick. It should be understood that other embodiments of the opticalsystem 10 may employ optical disks 12 of other thicknesses.

Referring now to FIG. 1, the optical system 10 further includes atracking control mechanism (not shown), which may utilize existingtechnology, such as a push-pull photodetector. The laser source 31irradiates a fine collimated beam preferably with a wavelength of lessthan 0.6 micron to 0.7 micron, and a beam diameter of approximately 1micron. Such a beam can be generated for instance by a soliton laser; alaser source using a self focusing medium or a non-linear optical mediumsuch as a photo refractive crystal; or any other suitable light sourcethat emits a fine collimated beam.

The two mirrors M1 and M2 are reflective. An advantage of the presentinvention is that the reflectivity of the mirrors M1 and M2 is notcritical since the difference in the reading intensities of the digits"1" and "0" is significant. In other terms, as described above relativeto FIGS. 2 and 3 the intensity of the light indicative of the digit "1"is substantially close to the intensity of the laser beam 37 which istransmitted through the disk 12 with no or minimal attenuation. On theother hand, the intensity of the light indicative of the digit "0" iszero or substantially zero since the laser beam 37 is blocked by theblock regions. Thus the difference in the reading intensities of thedigits "1" and "0" is substantially equal to the intensity of the laserbeam 37 and is therefore significantly higher than the difference in thereading intensities realized by existing optical systems.

In one embodiment the reflectivity of the mirrors M1 and M2 can be 95percent. Such tolerance in the reflectivity of the mirrors M1 and M2allows for a greater tolerance in the design of the optical system 10,thus contributing to a reduction in the components and manufacturingcost.

Mirrors M1 and M2 may have any desirable shape. In one embodimentmirrors M1 and M2 are identical and have a surface area of approximately1 mm². The distance between the centers of mirrors M1 and M2 depends onthe thickness of the optical disk 12. Such distance is not criticalsince the present optical system 10 does not utilize a focused beam butrather a collimated beam. The laser beam 37 travels parallel to the disksurface at a height ranging from about 0.2 mm to 1.0 mm therefrom.

In a preferred embodiment the mirrors M1 and M2 are disposedsymmetrically relative to the disk 12. Mirror M1 is positioned at anangle of +45 degrees relative to the surface of the disk 12, whilemirror M2 is positioned at an angle of -45 degrees relative to the disksurface. In this embodiment the laser beam 37 can travel normally to thedisk surface.

In another embodiment the mirrors M1 and M2 can be physically connectedtogether to be moved independently from the laser source 31 and thephoto-detector 33. In such a design, the mirrors M1 and M2 can be movedradially without much concern about alignment, since the light beamtravels parallel to the surface of the disk 12. As used herein, a mirroris an optical reflective component.

In still another embodiment mirror M1 is positioned at an angle "α"relative to the disk surface, and mirror M2 is positioned at an angle"β" relative to the disk surface, such that:

    β≈(90°-α).

In this alternative embodiment the mirrors M1 and M2 are not disposed inregistration relative to each other, i.e., symmetrically with respect tothe disk surface. Mirrors M1 and M2 are offset such that the laser beam37 reflected by mirror M1 is captured by mirror M2 and travels parallelto the disk surface.

In yet another embodiment the mirrors M1 and M2 are rotatable and theirangular dispositions relative to the disk surface remain complementary.In addition the first and second optical arms 22, 24 can moveindependently of each other, such that the distance between the mirrorsM1 and M2 varies in order for the laser beam 37 reflected by mirror M2to travel along a path parallel to the disk surface.

With reference to FIG. 6, it illustrates a magneto-optic system 100according to the present invention. The system 100 uses a similar basicdesign to that of the system 10 (FIG. 1) and includes several similarcomponents. The operation of the system 100 is relatively similar tothat of the system 10 and is further capable of writing data onto amagneto-optic disk 112.

The system 100 includes a magnet 115, such as an electromagnet or apermanent magnet, for writing data onto the disk 112. The magnet 115 iscylindrically shaped, and is hollow along its axial length for allowinga light beam to pass through the magnet 115. The magnet 115 is securedto one end of mirror M1 such that the laser beam 37 reflected by mirrorM1 passes through the hollow center of the magnet 115. The magnet 115does not have a significant effect when the system 100 reads dataalready recorded on the disk 112. When the system 100 is in the processor reading data it functions in the same manner as described above inrelation to system 10.

When it is desired to write onto the disk 112, the laser source 31increases the intensity of the laser beam sufficiently so that it heatsa magneto-optic data substrate 154 (FIG. 7) of the disk 112 to acritical temperature, around its Curie temperature, as is known in thefield. As the critical temperature is reached, the magnetic domain fieldstrength of the magneto-optic data substrate 154 is reduced to close tozero. An external magnetic field is then applied to the magneto-opticdata substrate 154 using the magnet 115 to change the domain to record aone or a zero.

The arrows in the magneto-optic data substrate 154 are representative ofan illustrative magnetic domain that corresponds to the data pattern ofFIG. 3.

With reference to FIG. 7 the magneto-optic disk 150 is either fully orpartially transmissive to the light beam 37. The magneto-optic disk 150is formed of a plurality of generally transmissive superposed layers.The first layer is a substrate 152 which may be similar in compositionto the substrate 40 of FIG. 1. A data magneto-optic data substrate 154is formed or deposited on the substrate 152. In a preferred embodimentthe data magneto-optic data substrate 154 is, or may be coated with oneof the various writeable optical storage films such as WORM media, orone of the various erasable optical storage films such as phase change,or magneto-optical (WREM) media.

Any type of transmissive phase change films, substrates or rare earthtransition metals may be used as the magneto-optic data substrate 154,or as part of the magneto-optic data substrate 154. In one embodimenttwo or more layers of different transmissive phase change films orsubstrates may be superposed to form the magneto-optic data substrate154. The magneto-optic data substrate 154 may be vacuum deposited byknown sputtering techniques, onto the substrate 152, to a thicknesspreferably ranging between 5 nm and 60 nm.

An optional light transmissive protective undercoat 153 may be depositedbetween the substrate 152 and the magneto-optic data substrate 154. Thisprotective undercoat 153 may be for instance made of aluminum nitride(AIN) or any other suitable material. A light transmissive protectiveovercoat 155 may be formed on top of the magneto-optic data substrate154. The overcoat 155 may have a similar composition to that of theundercoat 153, and is approximately 20 nm thick. Another transmissiveprotective layer 156 may optionally be formed on top of the overcoat155. The protective layer 156 may be made of glass, plastic, or anyother suitable polymer material.

FIG. 8 illustrates yet another data storage medium or disk 160 which isa combination of the optical disk 12 and the magneto-optic disk 112,made according to the present invention. The disk 160 may be used withany of the optical systems, i.e., the optical system of FIG. 1 and themagneto-optic system of FIG. 6, described herein.

The disk 160 is similar to the magneto-optic disk 150 of FIG. 7 bututilizes a combination optical/magneto-optic data substrate 165 insteadof the magneto-optic data substrate 154. Like the data substrate 42 ofFIG. 2, the data substrate 165 includes a pattern of pass regions (i.e.,167) and block regions (i.e., 168, 170). As previously described inrelation to the data substrate 42 of FIG. 2, the block regions 168, 170include light reflective layers 173, 177, respectively. Similar to thedata substrate 154 of FIG. 7, the data substrate 165 is formed of one ormore magneto-optic layers for generating a magnetic domain illustratedby the arrows.

The data substrate 165 includes a combination of ROM, WORM, and / orWREM erasable media. In one design different types of materials areformed on designated tracks of the disk 160. As a result, the disk 160may be used as ROM, WORM and/or WREM media.

It should be understood that the geometry, compositions, and dimensionsdescribed herein may be modified within the scope of the invention. Forinstance, the inventive concept of the present invention may be extendedto optical and magneto-optic media with multiple data layers. Othermodifications may be made when implementing the invention for aparticular environment.

FIG. 9 is a schematic view of an optical data storage system 200according to the present invention. The system 200 includes an opticalhead 203 and a data storage medium such as a CD ROM disk 205. The disk205 is removably mounted on a spindle 14. The spindle 14 is rotatablysecured to a motor 16, which, in turn, is secured to a chassis 18. Themotor 16 rotates the spindle 14 as well as the disk 200 around an axisin the direction of the arrow A.

The optical head 203 is mounted on a platform 26, which, in turn, issecured to the chassis 18 An important feature of the present inventionis that the head 203 does not move mechanically but instead steers ordiffracts a light beam, such as the laser beam 37 by holographic oracousto-optical methods. In addition, since it would be desirable toreduce the overall size of the system 200 so that it has near planardimensions, the optical head 203 is positioned as close as possible tothe disk 205, such that the angle "Θ" (FIG. 10A) formed between thelaser beam 37 and a plane parallel to the land (i.e., 220) surface canvary between substantially 1 or 2 degrees and 89 degrees. The angle "Θ"can sufficiently large (for example 45 degrees) so that the laser beam37 is capable of sweeping the entire surface of the disk 205, betweenits inner diameter track (ID) and its outer diameter track (OD) bysteering or diffracting the laser beam 37 for a few degrees. The closerthe head 203 is to the disk 205, the smaller the steering or diffractionangle becomes.

With further reference to FIG. 10A, the optical head 203 generallyincludes a light source such as a laser source 208, a beam steeringelement 210, a beam splitter 212, and a photo-detector 214. The disk 205contains a pattern of spiral, or alternatively concentric lands (e.g.,220, 221, 222, 223) and adjacent pits (e.g., 225, 226, 227). Each pit iscontinuous and defines a concentric circle along a track. Similarly,each land is continuous and defines a concentric circle along a track.

Each pit, for instance the pit 225, includes a ridge 230 facing theoptical head 203, which is generally normal to an incident laser beam37. When it is desired to record a data bit, for instance a "1" onto thedisk 205, the corresponding ridge 230 is coated with a reflective layer232. As a result, the absence of the reflective layer 232 on the ridge230, as is illustrated relative to the pit 227, indicates a "0" databit.

In a preferred mode of operation, the optical head 203 is fixedlymounted onto the platform 26, and remains stationary throughout theentire operation of the optical system 200. The laser source 208generates the light or laser beam 37 which impinges upon, and isreflected by the ridge 230. If the ridge 230 were not coated with areflective layer 232 as is illustrated relative to the pit 227, then thelight beam 37 is diffracted by the pit 227. The difference in thereflectivity of the light beam 37 by the coated and uncoated ridges 230is therefore noticeably great and provides a clear reading of therecorded data.

The optical system 200 offers several advantages over existing systems.For instance, the optical system 200 eliminates the requirement for afocusing mechanism, thus reducing the number of components, simplifyingthe system manufacture and operation and improving its performance, andreducing its overall cost. In addition, since the optical head 203 isstationary the system 200 is more stable and generates less noise thusoptimizing the signal to noise ratio.

The various components of the optical system 200 will now be describedin more detail. FIG. 10A provides a cross-sectional view of the opticaldata storage medium or disk 205 according one embodiment of the presentinvention. The disk 205 includes a data substrate 240 formed on a lowersurface of the disk 205. The data substrate 240 may be made of anysuitable material such as glass, polycarbonate or another suitablepolymer material. An optional undercoat layer (not shown) may be formedunderneath the data substrate 240 to provide added mechanical supportand protection. A suitable overcoat protective layer 243 made of knownmaterial is formed on top of the data substrate 240. An optionalprotective undercoat layer is preferably formed on the surface of thedata substrate 240.The overcoat layer 243, and/or the undercoat layermay be made for instance of aluminum nitride (AIN) or any other suitablematerial to provide adequate protection to the data substrate 240.

The data substrate 240 is patterned, for instance by photoetching, toform the lands 220, 221, 222, 223 and the pits 225, 226, 227. Each landis generally flat and may have a length of approximately equal to, orless than one bit length (i.e., between 0.7 μm and 4 μm), though otherdimensions are also foreseeable. In one embodiment the lands are formedfor instance by first patterning the data substrate 240 and then byremoving regions of the data substrate 240, such as by photo-etching orother known techniques. In one embodiment all the lands are formed atthe same or similar depth or distance relative to the upper surface 250of the data substrate 240. It should however be clear that the pits maybe formed at different depths relative to the upper surface 250. Whilethe lands are illustrated to be flat, it should be clear that some orall of the lands may be non-planar or with roughened or patterned lightincident surfaces.

The pits are regions that are embossed or raised relative to theadjacent lands. In one embodiment each pit is formed of an outer ridge,such as the ridge 230, which is angled relative to the adjacent land,i.e., 221, 222, 223. The angular disposition, that is the angle definedbetween the surface of the ridge 230 and the adjacent land 220 (i.e.,approximately equal to "180°-Θ"), where the angle Θ may be set to, orexceeds a few degrees, such that the ridge 230 is substantially normal(i.e., perpendicular) to an incident laser beam 37.

The surface of the ridge 230 may be flat and smooth, or alternatively itmay be roughened, so that when it is not coated with the reflectivelayer 232 the light beam is diffracted by the ridge 230, thus furtherincreasing the difference in reflectivity of the laser beam 37 betweenthe coated ridges and the uncoated ridges. The ridges 230 areselectively coated with reflective layers, such as 232, 236 to recorddesired data bits. The reflective layers may be made of any suitablereflective material such as aluminum metal.

The reflective layers have a generally flat reflective surface that isgenerally parallel to the ridge 230. As a result, when the incidentlaser beam 37 impinges upon the reflective layers 232, 236, it isreflected along substantially the same optical path as the incidentlaser beam 37, back toward the optical head 203 where its intensity isdetected and as it will be described later. The optical system 200further includes a tracking control mechanism (not shown), which mayutilize existing technology, such as a push-pull photodetector.

In one embodiment all the pits 225, 226, 227 are substantially similarin shape, dimensions and configuration. However, in another embodimentthe pits are not similar. For instance, the angular disposition (i.e.,approximately equal to "180°-Θ") of the outermost pits along the outerdiameter track (OD) is different than the angular disposition of theinnermost pits along the inner diameter track (ID). In addition, theangular dispositions of the intermediate pits between the outer andinner diameter tracks (OD) and (ID), respectively, vary. For instance,in one embodiment the angular dispositions of the intermediate pitsgradually and progressively increase between the angular dispositions ofthe outer and inner diameter tracks (OD) and (ID), respectively.

Referring now to the optical head 203, the laser source 208 emits a finecollimated beam preferably with a wavelength of less than 0.6 micron to0.7 micron and a beam diameter of approximately 1 micron. Such a beamcan be generated for instance by a soliton laser; a laser source using aself focusing medium or a non-linear optical medium such as aphoto-refractive crystal; or any other suitable light source that emitsa fine collimated beam.

The beam steering element 210 causes a laser beam 37L emited from thelaser source 208 to be swept optically across the entire (oralternatively across one or more selected segments) of the disk 205.This sweeping action is carried out using a holographic, anacousto-optical or a combination holographic/acousto-optical sweepingtechnique.

When holographic sweeping is used, the beam steering element 210includes a holographic crystal inside of which a holographic grating isrecorded by means of laser beams 37L and 37H each having a predeterminedwavelength. The laser beam 37L from the laser source 208 is deflected bythe grating, and, by changing the wavelength of the laser beams 37L and37H, the holographic grating changes accordingly, causing the resultinglaser beam 37 to be steered between the outer and inner diameter tracksOD and ID, respectively, as desired. The holographic grating, recording,and deflecting techniques are generally known and described in "OpticalBeam Deflection Using Dynamic Volume Reflection Gratings" in Optical andQuantum Electronics 21 (1989), pages 151-154; G. T. Sincerbox and G.Rosen, Applic. Opt. 22 (1983), 690; and J. P. Herriau, A. Delboulbe, J.P. Huignard, G. Rosen, and G. Pauliat, IEEE J. Lightwave Technol. LT-4(1986) 905, all of which are incorporated herein by reference.

When acousto-optical sweeping is used, the beam steering element 210includes an acoustic crystal or a Bragg cell composed for instance ofLiNbO₃, which deflects the laser beam 37L when an acoustic wave(indicated by the reference numeral 37H) impinges upon the acousticcrystal, causing the resulting laser beam 37 to be steered between theouter and inner diameter tracks OD and ID, respectively, as desired. Theacousto-optical technique is known and described in "Scanning BeamCollimation Method for Measuring DynamicAngle Variations Using anAcousto-Optic Deflector" by Lijiang Zeng, et al., 1662 Opt. Eng. 35(2)1662-1663 (June 1996), which is incorporated herein by reference.

The incident beam 37, or a part thereof is reflected by either thereflective layer 232 or the uncoated ridge 230, back toward the opticalhead 203 and impinges upon the beam splitter 212. The beam splitter 212separates the incident beam 37 and the beam reflected by the disk 205,and deflects the reflected beam into a beam 37D which is detected by thephoto-detector 214. The photo-detector 214 detects the intensity of thedeflected laser beam 37D. If the intensity of the deflected beam 37D isgreater than a predetermined level, the optical head 203 determines thatthe incident laser beam 37 was reflected by a ridge 230 with areflective layer 232, and as a result reads a predetermined data bit,such as a "1". If on the other hand the intensity of the deflected beam37D is less than a predetermined level, the optical head 203 determinesthat the incident laser beam 37 was not reflected by a ridge 230 with areflective layer 232, and as a result reads a predetermined data bit,such as a "0".

With reference to FIG. 9, the optical system 200 may include anotheroptical head 203A positioned above an upper surface 251 of the disk 205so that the optical heads 203 and 203A may now read data from the lowersurface 252 of the disk 205 as well as the upper surface 251 of the disk205, respectively. In such an embodiment the upper surface 251 ispatterned with lands and pits as described herein in relation to thelower surface 252.

In another embodiment the optical system 200 includes one or two opticalheads 203, 203A, each capable of translating up and down vertically, inthe direction of the arrow C. In still another embodiment the platform26 may slide laterally in the direction of the arrow B. In yet anotherembodiment one or both optical heads 203, 203A are capable of slidingvertically in the direction of the arrow C, and the platform 26 iscapable of sliding laterally in the direction of the arrow B.

In a further embodiment, the reflective layers 232, 236 (FIG. 10A) arenot necessarily flat and may be concave or convex, so long as theincident laser beam 37 is reflected generally back toward the opticalhead 203 to be detected thereby. In a further embodiment the lasersource 208 and the laser steering element 210 are disposed remotely fromthe beam splitter 212 and photo-detector 214 so that the incident laserbeam 37 is not necessarily normal to the reflective layers 232, 236provided the reflected laser beam impinges upon the beam splitter 212for detection by the photo-detector 214.

In another embodiment the optical system 200 further includes anoptional isolator 255 positioned between the laser source 208 and thebeam steering element 210 so as to attenuate any residual laser beamwhich is reflected back toward the laser source 208.

In still another embodiment the beam steering function is carried outholographically as well as by means of acousto-optical methods. In sucha design, the laser beam 37L from the laser source 208 is firstdeflected using the acousto-optical method described herein, and thedeflected laser beam is further deflected using the holographictechnique described herein. Such double deflection will permit theoptical head 203 to be positioned in closer proximity to the disk 205.

FIG. 10B illustrates another configuration of a data layer 276 formingpart of the disk 205. The data layer 276 has a moth eye configurationwherein the pits, i.e., 278, 279, 280 have a conical configuration(i.e., a triangular cross-section). Each pit includes a ridge, i.e.,281, similar to ridge 230, which ridge 281 may or may not be coated witha reflective coating, i.e., 282, 286, which reflective coating has asubstantially similar function and design to the reflective coatings232, 236 shown in FIG. 10A. The reflective coating, i.e., 282, 286, maycover the entire surface of the ridges 230 or a selected portionthereof.

It should be understood that the geometry, compositions, and dimensionsdescribed herein may be modified within the scope of the invention. Forinstance, the inventive concept of the present invention may be extendedto optical and magneto-optical media with multiple data layers.Furthermore, the optical head 203 may alternatively or additionally bemoved pivotally. Other modifications may be made when implementing theinvention for a particular environment.

FIG. 11 is a schematic view of an optical data storage system 300according to the present invention. The system 300 includes an opticalhead 310 and a data storage medium such as a CD ROM disk 205. The disk205 is removably mounted on an axle 314. The axle 314 is fixedly securedto a chassis 18. In an alternative embodiment the optical head 310 maybe connected to a platform 26 secured to the chassis 18 or to any othersuitably located support structure.

An important feature of the present invention is that neither theoptical head 310 nor the disk 205 move mechanically. Instead, an opticalbeam, such as a light or laser beam 37 is steered or diffracted byholographic or acousto-optical methods. In addition, since it would bedesirable to reduce the overall size of the system 300 so that it hasnear planar dimensions, the optical head 310 may be positioned as closeas possible to the disk 205, such that the angle "Θ" (FIG. 12) formedbetween the laser beam 37 and a plane parallel to the land (i.e., 220)surface is small (i.e., a few degrees), but is also large enough so thatthe laser beam 37 is capable of sweeping the entire surface of the disk205, between its inner diameter track (ID) and its outer diameter track(OD) by steering or diffracting the laser beam 37 by a few degrees. Thecloser the optical head 310 is to the disk 205, the smaller the steeringor diffraction angle becomes.

With further reference to FIG. 12, the optical head 310 generallyincludes an optical source such as a laser source 208, a beam steeringelement 210, a beam splitter 212, and a photo-detector 214. The disk 205contains a pattern of spiral, or alternatively concentric lands (e.g.,220, 221, 222, 223, 224) and pits (e.g., 225, 226, 227, 228). Each pitis continuous and defines a concentric circle along a track. Similarly,each land is continuous and defines a concentric circle along a track.

Each pit, for instance the pit 225, includes a ridge 230 which isgenerally normal to an incident laser beam 37. When it is desired torecord a data bit, for instance a "1" onto the disk 205, thecorresponding ridge 230 is coated with a reflective layer 232. As aresult, the absence of the reflective layer 232 on the ridge 230, as isillustrated relative to the pit 227, indicates a "0" data bit.

In a preferred mode of operation, the optical head 310 remainsstationary throughout the entire operation of the optical system 300.The laser source 208 generates the light or laser beam 37 which impingesupon, and is reflected by the ridge 230. If the ridge 230 were notcoated with a reflective layer 232 as is illustrated relative to the pit227, then the light beam 37 is partly reflected or diffracted by the pit227. The difference in the reflectivity of the light beam 37 by thecoated and uncoated ridges 230 is therefore noticeably great andprovides a clear reading of the recorded data bits.

The optical system 300 offers several advantages over existing systems.For instance, the optical system 300 eliminates the requirement for afocusing mechanism, thus reducing the number of components, simplifyingthe system manufacture and operation, improving its performance, andreducing its overall cost. In addition, since the optical head 310 andthe disk 205 are stationary the system 300 is more stable and generatesless noise thus optimizing the signal to noise ratio.

The various components of the optical system 300 will now be describedin more details. FIG. 12 provides a cross-sectional view of the opticaldata storage medium or disk 205 according one embodiment of the presentinvention. The disk 205 includes a data substrate 240. The datasubstrate 240 may be made of any suitable material such as glass,polycarbonate or another suitable polymer material. An optionaloverercoat protective layer (not shown) may be formed on top of the datasubstrate 240. A suitable protective undercoat layer 243A is formedunderneath the data substrate 240, to provide added mechanical supportand protection. The undercoat layer 243, and/or the overcoat layer maybe made for instance of aluminum nitride (AIN) or any other suitablematerial to provide adequate protection to the data substrate 240.

The data substrate 240 is patterned, for example by photoetching, toform the lands 220, 221, 222, 223, 224 and the pits 225, 226, 227, 228.Each land is generally flat. In one embodiment the lands are formed forinstance by first patterning the data substrate 240 and then by removingregions of the data substrate 240, such as by photo-etching or otherknown techniques. In one embodiment all the lands are formed at the sameor similar depth or distance relative to the surface 250 of the datasubstrate 240. It should however be clear that the pits may be formed atdifferent depths relative to the surface 250. While the lands areillustrated to be flat, it should be clear that some or all of the landsmay be non-planar or with roughened or patterned light incidentsurfaces.

The pits are regions that are embossed or raised relative to theadjacent lands. In one embodiment each pit is formed of an outer ridge,such as the ridge 230, which is angled relative to the adjacent land,i.e., 221, 222, 223. The angular disposition, that is the angle definedbetween the surface of the ridge 230 and the adjacent land 220 (i.e.,approximately equal to "180°-Θ"), where the angle Θ may be set to, orexceeds a few degrees, such that the ridge 230 is substantially normal(i.e., perpendicular) to an incident laser beam 37.

In a preferred embodiment, the angles formed between the ridges 230 andthe adjacent lands (or the data substrate surface 250) changes with theposition of the tracks along which the pits are formed in order tomaintain a substantially 90 degree angle with the incident optical beam37. For instance, the angular disposition (i.e., approximately equal to"180°-Θ") of the outermost pits along the outer diameter track (OD) isdifferent than the angular disposition of the innermost pits along theinner diameter track (ID). In addition, the angular dispositions of theintermediate pits between the outer and inner diameter tracks (OD) and(ID), respectively, vary. For instance, in one embodiment the angulardispositions of the intermediate pits gradually and progressivelyincrease between the angular dispositions of the outer and innerdiameter tracks (OD) and (ID), respectively. In another embodiment allthe pits 225, 226, 227, 228 are substantially similar in shape,dimensions and configuration.

The surface of the ridge 230 may be flat and smooth, or alternatively itmay be roughened, so that when it is not coated with the reflectivelayer 232 the light beam is diffracted by the ridge 230, thus furtherincreasing the difference in reflectivity of the laser beam 37 betweenthe coated ridges and the uncoated ridges. The ridges 230 areselectively coated with reflective layers, such as 232, 236, 237 torecord desired data bits. The reflective layers may be made of anysuitable reflective material such as aluminum metal.

The reflective layers 232, 236, 237 have a generally flat reflectivesurface that is generally parallel to the ridge 230. As a result, whenthe incident laser beam 37 impinges upon the reflective layers 232, 236,237 it is reflected along substantially the same optical path as theincident laser beam 37, back toward the optical head 310 where itsintensity is detected and as it will be described later. The opticalsystem 300 further includes a tracking control mechanism (not shown),which may utilize existing technology, such as a push-pullphotodetector.

Referring now to the optical head 310, the laser source 208 emits a finecollimated beam preferably with a wavelength of less than 0.6 micron to0.7 micron and a beam diameter of approximately 1 micron. Such a beamcan be generated for instance by a soliton laser; a laser source using aself focusing medium or a nonlinear optical medium such as aphoto-refractive crystal; or any other suitable light source that emitsa fine collimated beam.

The beam steering element 210 causes a laser beam 37L from the lasersource 208 to be swept optically across the entire (or alternativelyacross one or more selected segments) of the disk 205. This sweepingaction is carried out using a holographic, an acousto-optical or acombination holographic I acousto-optical sweeping technique.

One such acousto-optical sweeping technique according to the presentinvention will now be described in relation to FIGS. 13 through 16. FIG.13 illustrates an acousto-optical crystal forming part of the beamsteering element 210 of the optical storage system 300 of FIGS. 11 and12, for controlling the sweeping or deflection of the optical or laserbeam 37L emanating from the laser source 208, in an X direction.

A crystal 330 may be an elasto-optical crystal used in conjunction withthe acousto-optical sweeping technique, or a photo-refractive crystalused in conjunction with the holographic sweeping technique. When thecrystal 330 is an elasto-optic crystal as used in a Bragg cell, it maybe composed for example of LiNbO₃. The acousto-optical crystal 330deflects the laser beam 37L (FIG. 14). Two acoustic waves AWx have thesame or substantially similar wavelength, intensity or amplitude, asthey may originate from the same acoustic source and are thereaftersplit into two acoustic waves AWx.

The acoustic waves AWx impinge simultaneously upon the crystal 330 fromtwo opposite sides 335, 337, along the X direction. The acoustic wavesAWx are generally normal to the sides 335, 337. The acoustic waves AWxinterfere and form an acoustic standing wave pattern (or grating) whichis normal to the incident acoustic waves AWx. Due to the elasto-opticeffect of the crystal 330, the optical refractive index "n" of thecrystal 330 will be modulated by the interference pattern of theacoustic waves AWx.

The optical refractive index "n" depends on the density of the materialforming the crystal 330, and results in an optical grating inside thecrystal 330, which is referred to as an optic phase grating 339. Theoptic phase grating 339 includes patterns that are normal to theacoustic waves AWx, and causes the impinging optical beam 37L to bedeflected in the X-direction as the optical beam 37.

As illustrated in FIG. 14, the optical beam 37L defines an angle ofincidence "a" relative to the patterns of the optic phase grating 339,and the deflected optical beam 37 defines an angle of deflection "b"relative to the same patterns. By changing the wavelength of theacoustic waves AWx, the acoustic interference of the acoustic waves AWxchanges, resulting in a corresponding change in the acoustic standingwave patterns and the optic phase grating 339, which ultimately causesthe optical beam 37L to be deflected along a different deflection angle"c". Consequently, it is now possible to cause the optical beam 37 to beswept, and to scan the disk 205 in the X direction.

FIG. 15 illustrates a technique for controlling the sweeping ordeflection of the optical or laser beam 37L in the Y direction. Twoacoustic waves AWy have the same or substantially similar wavelength,intensity or amplitude, as they may originate from the same acousticsource and are thereafter split into two acoustic waves AWy.

The acoustic waves AWy impinge simultaneously upon the crystal 330 fromtwo opposite sides 345, 347, along the Y direction. The acoustic wavesAWy are generally normal to the sides 345, 347. The acoustic waves AWyinterfere and form an acoustic standing wave pattern (or grating) whichis normal to the incident the acoustic waves AWy. Due to theelasto-optic effect of the crystal 330, the optical refractive index "n"of the crystal 330 will be modulated by the interference pattern of theacoustic waves AWy.

The optical refractive index "n" results in an optic phase grating 350.The optic phase grating 350 includes patterns that are normal to theacoustic waves AWy. The optic phase grating 350 causes the impingingoptical beam 37L to be deflected in the Y-direction as the optical beam37.

As illustrated in FIG. 16, the optical beam 37L defines an angle ofincidence "d" relative to the patterns of the optic phase grating 350,and the deflected optical beam 37 defines an angle of deflection "e"relative to the same patterns. By changing the wavelength of theacoustic waves AWy, the acoustic interference of the acoustic waves AWychanges, resulting in a corresponding change in the acoustic standingwave patterns and the optic phase grating 350, which ultimately causesthe optical beam 37L to be deflected along a different deflection angle"f". Consequently, it is now possible to cause the optical beam 37 to beswept, and to scan the disk 205 in the Y direction.

The optical head 300 utilizes the crystal 330 and the acoustic waves Awxand AWy simultaneously, and includes a control circuit (not shown) thatregulates the sweeping action, as desired along the plane containing theX and Y axes (2 dimensional sweeping).

The same or similar technique described above in relation to theacousto-optic sweeping method can be used as a holographic sweepingtechnique by replacing the acousto-optical crystal 330 with one or morephoto-refractive crystals, for example LiNbO₃, BaTiO₃. The holographicgrating inside the crystal 330 is then recorded by means of two coherentrecording beams that impinge upon the crystal 330 from the samedirection and that have the same wavelength. The laser beam 37L from thelaser source 208 is deflected by the holographic grating, and, bychanging the wavelength of the two coherent recording beams, theholographic grating changes accordingly, causing the resulting laserbeam 37 to be steered between the outer and inner diameter tracks OD andID, respectively, along the plane containing the X and Y axes, asdesired.

Referring now to FIG. 12, the incident beam 37, or a part thereof isreflected by either the reflective layer 232 or the uncoated ridge 230,back toward the optical head 310 and impinges upon the beam splitter212. The beam splitter 212 separates the incident beam 37 and the beamreflected by the disk 205, and deflects the reflected beam into a beam37D which is detected by the photo-detector 214. The photo-detector 214detects the intensity of the deflected laser beam 37D. If the intensityof the deflected beam 37D were greater than a predetermined level, theoptical head 310 determines that the incident laser beam 37 wasreflected by a ridge 230 with a reflective layer 232, and as a resultreads a predetermined data bit, such as a "1". If on the other hand theintensity of the deflected beam 37D is less than a predetermined level,the optical head 310 determines that the incident laser beam 37 was notreflected by a ridge 230 with a reflective layer 232, and as a resultreads a predetermined data bit, such as a "0".

Reference is now made to FIG. 18, which illustrates one structuralembodiment of the optical head 301. The axle 314 is stationary,cylindrically shaped, and passes through an opening in the geometriccenter of the disk 205. The beam splitter 212 is secured co-axially ontop of, and relative to the axle 314. The beam splitter 212 ispreferably cylindrically shaped and is hollow throughout its axiallength. The beam splitter 212 has a reflective surface which is at leastpartly transmissive (or transparent) to the beam 37H from emanating fromthe laser source 208, and is at least partly reflective of the laserbeam 37 reflected back from the disk (205) surface.

The crystal forming part of the beam steering element 210 is mounted inproximity to the beam splitter 212, co-axially relative to the axle 314.The photo-redetector 214 includes a photo-detector ring which fitsco-axially relative to the axis of the axle 314.

The operation of the optical head 301 will now be described in moredetail. The laser source emits the laser beam 37H which passes throughthe photo-detector ring 214 and impinges upon the beam steering element210. The laser beam 37H is steered as described herein and passesthrough the beam splitter 212 which is at least partly transmissive tothe laser beam 37H. The steered laser beam 37 impinges onto the disk 205and is reflected back toward the splitter 212. The splitter 212 reflectsthe beam 37 off its outer surface into the beam 37D, toward thephoto-detector ring 214. The beam 37D impinges upon or is captured bythe photo-detector ring 214 for processing.

With reference to FIG. 11, the optical system 300 may include anotheroptical head 310A positioned below or above the disk 205 on a convenientstructure such as the platform 26. In addition, the optical head 310 maybe positioned below the disk 205 so that the optical head 300 may nowread data from a lower surface 252 of the disk 205 as well as an uppersurface 251 of the disk 205. In such an embodiment the upper surface 251and the lower surface 252 are patterned with lands and pits as describedherein.

While the optical system 300 has been described as being stationary, itshould be clear that the disk 205 may be rotatably secured to thechassis 18. Alternatively or additionally, the optical head 310 may bemovable or adjustable along the axle 314, the platform 26, or any otherstructure on which it is mounted. Furthermore, while the optical head310 is described as being mounted above the disk 205, the optical head310 may be located underneath the disk 205.

For example, the optical system 300 may include one or two optical heads310, 310A that are capable of translating up and down vertically. Inanother embodiment the platform 26 may translate laterally. In yetanother embodiment one or both optical heads 310, 310A are capable ofsliding vertically, and the platform 26 is capable of translatinglaterally.

In still another embodiment, the reflective layers 232,236 are notnecessarily flat and may be concave or convex, so long as the incidentlaser beam 37 is reflected generally back toward the optical 310 to bedetected thereby. In a further embodiment the laser source 208 and thelaser steering element 210 are disposed remotely from the beam splitter212 and photo-detector 214 so that the incident laser beam 37 is notnecessarily normal to the reflective layers 232, 236 provided thereflected laser beam impinges upon the beam splitter 212 for detectionby the photo-detector 214.

In another embodiment the optical system 300 further includes anoptional isolator 255 positioned between the laser source 208 and thebeam steering element 210 so as to attenuate any residual laser beamwhich is reflected back to the laser source 208.

In still another embodiment the beam steering function is carried outholographically as well as by means of acousto-optical methods. In sucha design, the laser beam 37L from the laser source 208 is firstdeflected using the acousto-optical method described herein, and thereflected laser beam is further deflected using the holographictechnique described herein. Such double deflection will permit theoptical head 310 to be positioned in closer proximity to the disk 205.

Referring now to FIG. 17 it illustrates an alternative beam steeringelement 210 which utilizes two separate acousto-optical crystals 360,361 and a reflective mirror 364. The acousto-optical crystal 360 causesthe optical beam 37L to be deflected along the X direction in an opticalbeam 37F, as explained herein. The mirror 364 reflects the optical beam37F in the direction of the acousto-optical crystal 361. Theacousto-optical crystal 361 causes the optical beam 37L to be deflectedalong the Y direction as explained herein.

It should be understood that the geometry, compositions, and dimensionsdescribed herein may be modified within the scope of the invention. Forinstance, the inventive concept of the present invention may be extendedto optical and magneto-optical media with multiple data layers.Furthermore, the optical head 310 may alternatively or additionally bemoved pivotally. Other modifications may be made when implementing theinvention for a particular environment.

What is claimed is:
 1. The optical data storage system for use with adata storage medium, the system comprising in combination:an opticalhead for steering an incident optical beam using an acousto-opticalmethod across the data storage medium wherein said incident optical beamis selectively reflected by the data storage medium to indicate a databit recorded on the storage medium; said optical head being positionedin proximity to the data storage medium, such that an incidence angle"Θ" formed between said incident light beam and a plane parallel to thedata storage medium is less than 90 degrees, and including:a lightsource for emitting said optical beam; a beam steering element forsteering said optical beam; a photo-detector for detecting a relativeintensity of a deflected optical beam for detecting said recorded databit; said beam steering element including an acousto-optical crystal forcontrolling a sweeping of said light beam; the data storage mediumincluding an innermost track and an outermost diameter track; saidincidence angle "Θ" allowing said incident light beam to selectivelysweep the surface of the data storage medium, between said innermosttrack and said outermost track; and the data storage medium furtherincluding a pattern of lands and pits; wherein at least some of saidpits include a ridge which is substantially normal to said optical beam.2. The system according to claim 1, wherein said acoustic-opticalcrystal is an elasto-optic crystal.
 3. The system according to claim 2,wherein said optical beam is a coherent laser beam having apredetermined wavelength.
 4. The system according to claim 1, whereinsaid incident optical beam is selectively reflected by the data storagemedium to indicate the type of data bits recorded on the storage medium.5. The system according to claim 1, wherein said beam steering elementincludes a first acousto-optical crystal for controlling the sweeping ofsaid optical beam in a first direction, and a second acousto-opticalcrystal for controlling the sweeping of said optical beam in a seconddirection.
 6. The system according to claim 1, wherein said beamsteering element includes a holographic crystal containing a holographicgrating; andwherein said holographic grating is recorded by means of twocoherent recording beams each having a predetermined wavelength.
 7. Thesystem according to claim 1, further including an isolator positionedbetween said optical source and said beam steering element.
 8. Anoptical data storage system for use with a data storage medium, thesystem comprising in combination:an optical head for steering anincident optical beam holographically across the data storage mediumwherein said incident optical beam is selectively reflected by the datastorage medium to indicate a data bit recorded on the storage medium;said optical head being positioned in proximity to the data storagemedium, such that an incidence angle "Θ" formed between said incidentlight beam and a plane parallel to the data storage medium is less than90 degrees, and including:a light source for emitting said optical beam;a beam steering element for steering said optical beam; a photo-detectorfor detecting a relative intensity of a deflected optical beam fordetecting said recorded data bit; said beam steering element including aholographic grating for controlling a sweeping of said optical beam; thedata storage medium including an innermost track and an outermostdiameter track; said incidence angle "Θ" allowing said incident lightbeam to selectively sweep the surface of the data storage medium,between said innermost track and said outermost track; and the datastorage medium further including a pattern of lands and pits; wherein atleast some of said pits include a ridge which is substantially normal tosaid optical beam.
 9. The system according to claim 8, wherein the datastorage medium includes an innermost diameter track, an outermostdiameter track, and a pattern of intermediate tracks therebetween;andwherein said incidence angle "Θ" allows said incident light beam toselectively sweep the entire surface of the data storage medium, betweensaid innermost diameter track, and said outermost diameter track. 10.The system according to claim 8, wherein said beam steering elementincludes a holographic crystal containing a holographic grating;andwherein said holographic grating is recorded by means of tworecording beams, with each beam having a predetermined wavelength. 11.The system according to claim 8, wherein said light beam is deflected bysaid holographic grating by changing said wavelength of at least one ofsaid two coherent recording beams for causing said laser beam to besteered across the data storage medium.
 12. The system according toclaim 8, wherein if the relative intensity of said deflected light beamexceeds a predetermined level, said optical head detects the presence ofa first data bit.
 13. The system according to claim 12, wherein if therelative intensity of said deflected light beam does not exceed apredetermined level, said optical head detects the presence of a seconddata bit.
 14. The system according to claim 8, further including anisolator disposed between said light source and said beam steeringelement to attenuate a portion of said reflected light beam that istransmitted to said beam splitter.
 15. The system according to claim 8,wherein the data storage medium includes an upper surface and a lowersurface;wherein said optical head is positioned below said lower surfaceof the data storage medium for reading data on said lower surface; andwherein the optical system further includes a second optical headpositioned above said upper surface of the data storage medium forreading data on said upper surface.
 16. The system according to claim15, wherein said optical head translates vertically in a directionsubstantially perpendicular to said medium.
 17. The system according toclaim 15, wherein said optical head is mounted on a platform thattranslates in a direction substantially radial to said medium.
 18. Thesystem according to claim 15, wherein said optical head is mounted on aplatform that moves about an axis parallel to an axis of rotation ofsaid medium.
 19. The system according to claim 8, wherein said opticalhead translates in a direction parallel to an axis of rotation of saidmedium.
 20. The optical data storage system according to claim 8,wherein said pattern of lands and pits is substantially spiral.
 21. Theoptical data storage system according to claim 8, wherein said patternof lands and said pattern of pits are substantially concentric.
 22. Theoptical data storage system according to claim 8, wherein said lands arepatterned along at least one circle that defines a track.
 23. Theoptical data storage system according to claim 20, wherein said landsare patterned along a plurality of concentric circles that defineconcentric tracks.
 24. The optical data storage system according toclaim 8, wherein said pits are patterned along at least one circle thatdefines a track.
 25. The optical data storage system according to claim20, wherein said pits are patterned along a plurality of concentriccircles that define concentric tracks.
 26. The optical data storagesystem according to claim 8, wherein said ridge is coated with areflective layer.
 27. The optical data storage system according to claim8, wherein said incidence angle is variable.
 28. The optical datastorage system according to claim 20, wherein said incidence anglevaries between approximately 1 degree and 45 degrees.